A backlight is a main component of a liquid crystal display device. The backlight includes a plurality of LED light strings (L1, L2, . . . Ln) and current sinks connected with the light strings respectively. The current sink is configured to control each of the LED light strings to emit light, meanwhile to adjust the current flowing in the light string to reach a preset current by detecting a voltage across a preset resistor R connected in series between the light string and a ground in the current sink and comparing the voltage with a reference voltage Vref, thus ensuring a stable lighting of the backlight.